Erosion in Sudden Contractions and Expansions Available to Purchase

ABSTRACT

Sand in produced oil and gas can cause severe erosion damage. A multitude of factors affect erosion severity. An approach which can consider most of the factors and accurately quantify the amount of material loss is of great significance for oil and gas producers to prediction erosion for oilfield geometries like sudden contractions and expansions. Previously, a comprehensive CFD-based erosion prediction procedure has been proposed at Erosion Corrosion Research Center (E/CRC) based on a systematic study of erosion for abrasive jets. The procedure has provided engineers with a powerful tool to conduct erosion study and derive the optimal operating conditions. Application and validation of this procedure for sudden contractions and expansions in this work further demonstrates the generalization and robustness of this CFD-based method. Limitations of current CFD codes for erosion simulation of these geometries have been also highlighted in the process. Attempts to overcome the limitations are discussed. Finally, insights of running erosion simulation utilizing CFD for such geometries are summarized.

INTRODUCTION

Sudden contractions and expansions are commonly found in wellbores and flow control lines. The geometries can experience erosion when the flow is entrained with solid particles. Accurate erosion predictions are required in order to ensure designs that can withstand throughout the expected lifetime. CFD is a powerful tool as it can consider many factors. It is often used to aid in erosion predictions and decision-making for the purpose of integrity management. There are many practices in the literature and most of them are claiming success in adopting a CFD approach to conduct erosion predictions^1-5. But, for sudden contractions and expansions geometries, Wong et al.⁶ found that erosion prediction using CFD can be quite good for large particle (198 µm) and predicting erosion in direct impact areas. While for smaller particle (38 µm) and erosion caused by secondary or high order impacts, CFD loses accuracy rapidly and significantly. They also doubted the accuracy of the implemented particle-turbulence interaction model. Fard et al.⁷ explained that current commercial CFD codes limit eddy size to cell size and hence can impact particle dispersion in the fluid. Zhang et al.⁸ followed his work and tried to use mesh size to control particle-turbulence interaction and made some preliminary modifications in the near wall region within a 2-D model which has improved predictions. However, the modifications are not straightforward and generalized. Recently, investigators at Erosion Corrosion Research Center (E/CRC) have found CFD results can be fortuitous and misleading for erosion predictions if the near wall region is inappropriately treated⁹. Thus, efforts have been directed to formulating the best practice for erosion simulation particularly with emphasis on the near wall treatment. Zhang et al.¹⁰ examined in detail of CFD predictions with different mesh configurations and models. It stressed out the importance of an appropriate first layer thickness in conducting erosion prediction. And, the appropriate first layer thickness is found to be on the order of particle size. As a further development of the work, Zhang et al.¹¹ modelled sand fines in elbows mounted in series by applying the findings and has observed the effect of cell size on particle dispersion and the resulting erosion. It was concluded that to capture correct erosion profiles larger cell sizes are required in the core region to facilitate particle dispersion as eddy size is effectively limited to cell size in the commercial CFD codes.